Hypertension is a common problem in the urban Black population of the United States. While information is available on the prevalence of hypertension, data on incidence has been difficult to obtain because of the asymptomatic nature of the disease and the necessity for repeat blood pressure measurements in large population samples. It is proposed that a sample of the Black population of Baltimore, screened for hypertension in 1973-1974 and identified as (a) normotensive (average DBP less than 95) (b) labile (average DBP greater than or equal to 95 in the field but less than 90 on clinic measurement) and (c) controlled hypertensive (average DBP less than 95, but on antihypertensive medication), be rescreened at home to identify incident cases. This would provide information on hypertension incidence rates as well as evaluation of therapy in the controlled hypertensives. Incident cases from the previously normotensive and labile groups, together with matched controls, would be invited to a clinic evaluation for case confirmation and to conduct a case-control analysis of selected potential etiologic factors and evidence of end-organ damage. Evaluation of the incident cases will allow investigation of such factors closer in time to the onset of the disease than allowed by the study of prevalent cases.